The present invention relates to a system for realizing a service to reproduce a stored media via a network in real time, such as a VOD (video on demand) service. More specifically, the invention relates to a system for properly using various service classes of a network for each service suitable for its characteristic.
The present invention also relates to a system for realizing a service to offer a media information stored in a server, to a user via a network in real time on his/her demand. In particular, the present invention is directed to a system for data such as managed in time series. Specifically, the invention is directed to a system for data having characteristic wherein the use of the data is managed by a time information such as a time stamp. Throughout this specification, these data will be referred to as real-time data.
In recent years, interactive video services have begun to be made fit for practical use due to the developments of high-speed, wide-band networks and digital image techniques. One of typical examples of such services is a VOD service. The VOD service is a service in which a video server for storing a video source therein is connected to a client basically in the form of one-to-one so that the video source is outputted from the video server generally on the client""s demand for reproduction, search, special reproduction or the like. It is assumed that most of the VOD services utilize an ATM (asynchronous transfer mode) for at least the key of a network. Furthermore, throughout this specification, video servers include a temporary memory type server, called a cache node or a network cache, in which a video is stored on or near a communication line set for transmitting the video information which is being offered to a user, and the same video is reused on another user""s demand.
In the ATM, a number of classes are provided. For example, in the ATM forum serving as an organization for establishing the trade standard of ATM, the following five classes are standardized. That is, there are CBR (Constant Bit Rate), RT-VBR (Real Time Variable Bit Rate), NRT-VBR (Non-Real Time Variable Bit Rate), ABR (Available Bit Rate) and UBR (Unspecified Bit Rate). Among these classes, the service class of CBR is generally used in the present circumstances since the video transmitting service as set forth above is a real time service.
Then, there will be considered the five service classes as set forth above. From the standpoint of a real-time characteristic, the qualities of two classes including the CBR and the RT-VBR, which are guarantee classes, are guaranteed. In addition, although the CBR has an extremely low probability of discarded cells and a high quality, the cost thereof is high since it does not use the statistical multiplexing effect which is considered to be particularly effective as a method for effectively utilizing bands in the ATM. The RT-VBR is cheaper than the CBR since it uses the statistical multiplexing effect, although the cell discarding characteristic thereof is not better than the CBR. On the other hand, although the real-time characteristics of the NRT-VBR, the ABR and the UBR are not guaranteed, it can be expected that the communication cost is greatly decreased because these services are the best effort services for effectively using space bands.
In the conventional image transmitting systems as set forth above, the transmitting quality is constant in the CBR. For example, consider the situation wherein a two-hour video is watched via the VOD. In general, as the required qualities for the communication call in the VOD, the following matters are guessed: a real-time characteristic for immediate offer, a low rate of discarded cells for ensuring the qualities of image and voice, and a low-cost communication for realizing to decrease the cost of a video service. From the points of the guarantees of the real time characteristic and the cell discarding characteristic, the CBR is selected as a premise.
In general, in the case of the CBR, a band is assigned at a peak cell rate in a call connecting procedure, and this band remains being constantly set while the call is set. The CBR has a good quality since communication is performed after sufficiently ensuring the band. However, since this system does not use the multiplexing effect, the communication cost is high. For example, consider the VOD as set forth above. It is required to set the call while the video is watched. Considering that an image is transmitted to a communication line of 155 Mbps by a MPEG system of 6 Mbps, an image of 25 lines can be simultaneously delivered. On this condition, the communication cost is set. Of course, since the cost for software is also required, it is important to reduce the communication cost. In the conventional systems, there is a problem of decreasing the cost.
In addition, in the conventional system, the video, which has been stored for the previous client, is reused when another client accesses thereto. However, since the storage capacity of the data storage unit is limited, it is required to successively erase videos having a low frequency in access. In this case, the erasing of videos must be performed for each video source. Therefore, in a case where another client accesses immediately after the video source is erased, it is required to perform the transmission via the CBR again, the aforementioned problems become worse.
Since video sources to be offered in VOD services do not include only movies put on the screens in movie theaters, but also include many categories of video sources such as TV movies, dramas and documentary films, and also include all the products which have been produced up to now since a movie has been made, the number thereof is extremely vast. On the other hand, since the memory capacity of a video server for storing such video sources is limited, it is impossible to store all the video sources in a single video server. Also, the quantity of information which is able to be read out of a single video server at the same time is limited. Therefore, in general, it has been considered to adopt a two-hierarchy configuration wherein video servers for storing video sources, which are expected that the frequency in access is high, are arranged at locations near the users every local area, and video servers for storing video sources, which are expected that the frequency in access is low, are arranged at a center remote from the users, or a multi-hierarchy configuration in accordance with the frequency in access.
Thus, in a case where video servers for storing video sources to be offered are dispersively arranged on a network, it is required to establish a communication line between a user and a video server nearest the user among video servers, which have stored video sources on the user""s demand, to transmit a video through the established communication line from the standpoint of communication cost. Conventional systems are designed that a user determines a video by a previously distributed video list or the like to directly designate the video. Therefore, after the user designates the video, it is enough to determine the optimum video server for the offer of the video to establish the communication line.
However, it is considered in the future that it will be possible for a user to establish a communication line between the user and the most terminal video server to finally determine a video, that the user wishes to view, while the user interactively accesses a video list displayed on a screen, a part of video sources prepared for preview, and a promotion video consisting of highlight scenes. In such a case, from the standpoints of the responsibility to the user and the communication cost, it is desired to store video lists or video information for preview in the terminal video servers. In this case, if the user actually attempts to establish a communication between the user and a video server having stored a video source, which contains a video that the user wishes to view, after the user determines the video, it is possible to establish the communication line when the communication network is crowded, so that it is not possible to offer the video to the user. In addition, when the number of services offered at the same time by the server for storing the video source reaches the performance limit of the server, it is possible to offer the video even if it is possible to establish a communication line. Thus, if a user attempts to ensure communication network resources and server resources after determining a video that the user wishes to view, the user may waste time for determining the video that the user wishes to view, so that it is extremely inconvenient for the user.
As mentioned above, although it is required to realize a service of a low call-discarding rate in order to realize the immediate offer of image in the conventional image transmitting system, there are problems of decreasing the costs of image transmitting services and of effectively utilizing communication resources.
It is therefore an object of the present invention to provide an information relay system and an information transmission system which can improve the efficiency of communication and which can decrease service costs.
In order to accomplish the aforementioned object, according to first aspect of the present invention, there is provided an information transmission system which comprises: first communication means having a guaranteed quality required to transmit a real-time information; second communication means different from the first communication means; means for transmitting a stored real-time information using the first communication means and for transmitting a real-time data using the second communication means, the real-time data being earlier than the real-time information transmitted by the first communication means; storage means for storing the information transmitted by at least the second communication means; and switching means for monitoring a period of time for reproducing the real-time information transmitted from the first communication means and a period of time for reproducing the real-time information stored in the storage means, and for switching the output of the real-time information transmitted from the first communication means, to the output of the real-time information transmitted from the storage means when the period of time for reproducing the real-time information stored in the storage means and transmitted from the second communication means elapses, so that the second communication means has a service class which does not always have a guaranteed quality required to transmit a real-time data, so as to realize an effective communication and to reduce the cost.
According to second aspect of the present invention, there is provided a real-time data transmitting system which comprises: first communication means having a guaranteed quality required to transmit a real-time data; second communication means different from the first communication means; transmitting means for transmitting a stored real-time data using the first communication means and for transmitting, using the second communication means, a real-time data which is earlier than the real-time data transmitted by the first communication means; storage means for storing the data transmitted by at least the second communication means; switching means for monitoring a reproducing time at which the real-time data transmitted from the first communication means is reproduced and a reproducing time at which the real-time data stored in the storage means is reproduced, and for switching the output of the real-time data transmitted from the first communication means, to the output of the real-time data transmitted from the storage means at the reproducing time at which the real-time data stored in the storage means and transmitted from the second communication means is to be reproduced; and reproduction means for receiving the output from the switching means to reproduce the real-time data, in order to realize an effective communication and to reduce the cost.
According to third aspect of the present invention, there is provided an information offer system which comprises: a plurality of data storage means, each storing a real-time data, the order of which is managed in time series; communication means for transmitting the real-time data; reproduction means for receiving and reproducing the real-time data; communication-network-resources management control means for managing communication resources of the communication means and for establishing a communication line between the data storage means and the reproduction means; storage-resources management control means for managing the kind of the real-time data stored in the data storage means, and for managing the number of real-time data being able to be transmitted by the data storage means at the same time, to determine one of the plurality of data storage means, by which a required real-time data is to be transmitted; and service control means for accepting a demand for services from a user, and for directing the communication-network-resources management control means and the storage-resources management control means to reserve resources on the basis of the state of resources obtained by the communication-network-resources management control means and the storage-resources management control means, the control means informing the user of only a real-time data, which is able to be offered immediately if selected, as a real-time data to be selected. In this system, the user is previously informed of real-time data which can be guaranteed to be offered immediately, so that the user can be select a real-time data among the informed real-time data. Therefore, it is possible to prevent the user from wasting time and labor for interactively selecting a required real-time data, so that it is possible to improve the facility for the user.
According to fourth aspect of the present invention, there is provided an information offer system which comprises: a plurality of data storage means, each storing a real-time data, the order of which is managed in time series; communication means for transmitting the real-time data; reproduction means for receiving and reproducing the real-time data; communication-network-resources management control means for managing communication resources of the communication means and for establishing a communication line between the data storage means and the reproduction means; storage-resources management control means for managing the kind of the real-time data stored in the data storage means, and for managing the number of real-time data being able to be transmitted by the data storage means at the same time, to determine one of the plurality of data storage means, by which a required real-time data is to be transmitted; and service control means for accepting a demand for services from a user, and for directing the communication-network-resources management control means and the storage-resources management control means to reserve resources on the basis of the state of resources obtained by the communication-network-resources management control means and the storage-resources management control means, the control means informing the user of a real-time data, which is able to be offered immediately if selected, as a real-time data to be selected, and the control means also informing the user of a real-time data wherein the reservation for resources sufficient to be offered immediately if selected, as a proposed real-time data which is not guaranteed to be offered immediately. In this system, the user is previously informed whether each real-time data is guaranteed to be offered immediately, so as to entrust the user with the determination whether the user runs the risk of wasting time and labor spent for interactively selecting a required real-time data, so that it is possible to improve the facility for the user.
According to fifth aspect of the present invention, there is provided a real-time data transmission system which comprises: first communication means having a guaranteed quality required to transmit a real-time data; second communication means different from the first communication means; means for transmitting a stored real-time data using the first communication means and for transmitting a real-time data using the second communication means, the real-time data being earlier than the real-time data transmitted by the first communication means; storage means for storing the data transmitted by at least the second communication means; and switching means for monitoring a period of time for reproducing the real-time data transmitted from the first communication means and a period of time for reproducing the real-time data stored in the storage means, and for switching the output of the real-time data transmitted from the first communication means, to the output of the real-time data transmitted from the storage means when the period of time for reproducing the real-time data stored in the storage means and transmitted from the second communication means elapses. According to this system, the second communication means uses a service class wherein the quality required to transmit a real-time data is not always guaranteed, so that it is possible to realize an effective communication to reduce the cost.
The aforementioned method is effective as a method for decreasing communication costs particularly when the service of storage type data such as VOD is offered in real time. A server system, which has received a demand for the offer of image, begins the offer of information to a receiving apparatus, which has transmitted the demand, in real time in the forward direction from the beginning of an information source such as a movie. As the quality in this case, the real-time characteristic and the low cell-discarding characteristic are required. Therefore, a class of a sufficiently guaranteed quality, such as the CBR, is used. On the other hand, at the same time as the offer of call, an information, which is not required to be offered in real time, is transmitted to the same receiving apparatus, for example, in the retrospective direction from the end of the information source, using a best effort communication class, such as the ABR and the UBR, as a second communication line, which is inexpensive although it is in non real time. The receiving apparatus transfers the real-time information transferred through the CBR, to the downward thereof as it is. On the other hand, the non-real-time information transferred through the best effort is being stored in a storage device, and the call for the high-quality class for real-time is released at the point of time when the non-real-time information reaches the same information as the real-time information. The information after that point of time is not required to be transferred through the CBR since it has been already stored in the storage device.
That is, if it is assumed that one information source is transferred, the portion of information transferred through the second-class communication line is unnecessary as the period of time for requesting to ensure the call of a high-quality class, and the transfer can be carried out at a low communication cost by that portion.
In particular, if the second communication line is the best effort class, the transfer can be extremely effectively carried out. That is, in the 6 Mbps MPEG information communication as set forth above, the transfer in the real-time information communication line must be carried out at a rate of 6 Mbps regardless of the band of the transmission line. However, in the best effort class used for the non-real-time information, the space bands except for the guarantee class are used with no useless to transfer the information. Therefore, if another user does not demand the offer of information, the best effort class can be used for the portion of 149 Mbps (155 Mbpsxe2x88x926 Mbps=149 Mbps). Therefore, it can be transferred using bands 20 times or more as large as those for the real-time information, so that it is the same that most of information is transferred via the best effort class. Of course, when another user demands the offer of information at the same time, such an efficiency can not be achieved. In general, in communication line designs, a band design is performed presupposing the a synchronism of calls such as a large crowd forming effect. Therefore, it is designed so as to have spare bands on the basis of a certain standard. From the standpoint of a band used efficiency, it can be expected that there are actually a great number of space bands for use in the ATM. For example, if the network is designed so that the band used efficiency is 50% at the cell level, the residual 50% can be used in the best effort class. As compared with the cost for transferring information via the CBR, the half thereof can be cheaply transferred at a cost of the best effort class.
In addition, such a multiplex transmission system, which uses a plurality of classes of different quality, is effective particularly in a core network using a large-capacity transmission line which has substantially the same capacity as that of a server system in which user""s demands are multiplexed, so that it seems that the multiplex transmission system is not always required for transmission lines of an access network to respective homes. In such a case, if a system for receiving the plurality of classes to store a non-real-time information is provided as an intermediate system such as a headend arranged between the core network and the access network, it is possible to provide a system in which the cost performance of the whole network is good.
Moreover, the aforementioned real-time data storing means divides the real-time data into a plurality of data segments to be managed, and determines the erasing order of the respective data segments on the basis of an elapsed period of time from the final access time of the stored real-time data and of a required reproduction period of time from the head of the real-time data to the end of the respective data segments when it is considered that the stored capacity is saturated. Therefore, if it is required to erase a video source having a low frequency in access when the storage capacity of the real-time storing means is saturated, each video is not successively erased, but the video is erased from the portion remote from the head of the video source, which is suitable for the transmission via the best effort class, so that it is possible to decrease the probability that the transmission via the CBR is required when it is accessed again.
As mentioned above, according to the present invention, a best effort service class, which is not so suitable for the transfer of a real-time data, can be effectively used for the transfer of the real-time data, and it is possible to improve the efficiency of communication and to decrease the cost for the offer of a service.
As mentioned above, according to the present invention, it is possible to prevent the user from wasting time and labor for interactively selecting a required real-time data, by informing the user of only real-time data, which are able to be guaranteed to be offered immediately, or by informing the user whether the respective real-time data are guaranteed to be offered immediately, so that it is possible to improve the facility for the user. Alternatively, the determination whether the user runs the risk is entrusted to the user, so that it is possible to improve the facility for the user.